Sound-absorbing structure



J. s. PARKlNsoN Erm. 2,270,825 soUND-ABsORBING STRUCTURE Filed Deo. l2, 1939 2 Sheets-Sheet l Jan. 20, 1942.

Jan' 20, l942 J. s. PARKlNsoN rs1-AL 2,270,825

SOUND-ABSORBING' STRUCTUR 2 Sheets-Sheet 2 Filed Dec. l2, 1939 Jo/.m SINEl/Sllioryon. Wz//gdm f. Lucius. 1

a am ATTORNEY n Patented Jan. 20, 1942 SOUND-ABSORBING STRUCTURE John s. Parkinson, North ramada, N. J., and William I. Lucius, Bronxville, N. Y., assignors to J ohns-Manville Corporation,

New York,

N. Y., a corporation of New York Application December 12, 1939, Serial No. 308,794

11 Claims. '(Cl. 181-42) The present invention relates to sound-absorbing structures. In its more specic phase the `invention is directed to the provision of soundhave found it necessary to provide test stands on which the motors may be mounted and run for extended periods of time under normal operating conditions. A conventional construction of a'stand for this purpose comprises a U-shaped structure in which the motor is mounted at the base of the U and the legs of the U form stacks or conduits, the air drawn by the propeller entering through one of the stacks and being expelled through the other.

The excessive noise involved, the noise being the same or substantially the same as that produced by the motor and propeller of a plane in flight, has long presented a serious problem, which heretofore has not been successfully solved. Notwithstanding that the sound is directed away from the ground by the stacks, a considerable percentage of the sound energy is deected downwardly into nearby areas or reflected from cloud banksor atmospheric layers` into more distant areas. -The problem has been greatly aggravated by the constant tendency to increase motor and propeller sizes.

The principal object of the present invention is to provide an improved sound-absorbing treatment for use in conjunction with test stands as referred to above or Where other similar-problems arise. A

Another object of the invention is the provision of a treatment as referred to above which will not appreciably impede the air ow through a conduit or stack, and which will be durable to withstand the highvelocity air flow through the stack, and other destructive forces to which it may be exposed. ,y

A further object of the invention is the provision of a sound-absorbing construction for the stacks of test stands and the like which may be readily assembled and rearranged as desired. 'A still further object of the invention is the provision of a stack or conduit which is subdivided into relatively narrow slots dened by relatively lightweight, removable, highly emcient sound-absorbing units.

Another object of the invention is the provision of a lightweight unit for the structure rereferred to above, including sound-absorbing material and sound-porous facings, the unit being arranged to be assembled with other similar units to provide a ribbon wall.

In one modification of the invention, an object is to provide a stack or conduit construction in which the outer walls, as well as inner soundabsorbing ribbon walls, are formed from similar lightweight Areadily assembled units.

Another modification of the invention has, as an object, the provision of an arrangement of units to provide particularly improved eiilciency in the absorption of sounds of high frequency.

Our invention will be more fully understood and further objects and advantages thereof will become apparent when reference is made to the more detailed description thereof which is to follow and to the accompanying drawings, in

which:

Fig. 1 is a vertical sectional view of a test stand including' stacks embodying the invention; Y

Fig. 2 is a plan view of a sound-absorbing unit employed in the construction of Fig. 1;

Fig. 3 is a sectional view taken on the line 3 3 of Fig. 2;

Fig. 4` is an enlarged detail `view of the portion indicated at A in Fig. 1;

Fig. 5 is an enlarged sectional view taken on the line 5-5 oi.' Fig. 1;

Fig. 6 is a sectional view similar to Fig. 3 illustrating a, modification of the invention;

Fig. 7 is a horizontal sectional view illustrating a modified stack construction in accordance with the instant invention;

Fig. 8 is a vertical sectional view of a stack construction embodying another modication of the invention; and

Fig. 9 is a detail view on an enlarged scale of the corner construction of the device of Fig. '7.

Referring now to the drawings, and particularly to Fig. 1, there is disclosed a test stand structure basically of a type now employed for the testing of airplane motors, propellers, and the like. It will be understood that the structure shown is merely. illustrative of a conven tional type of a test stand and that the invention lis equally applicable to other types and to structures for -other uses.

In the construction depicted, the test stand comprises a substantially U-shaped building including a motor mounting III in the room I2, forming the base of the U, and upstanding air intake and exhaust stacks I4 and I6, respectively. In accordance with conventional practice, the outer walls of the structure, including the stacks, may be formed of masonry, reinforced concrete, or the like. The structure may be of any desired dimensions, but for purposes of example, it may be stated that in a typical case the stacks are from 20 to 30 ft. high. and are, say, 20 x 20 ft. in horizontal cross section. A control room, not shown, is located adjacent the motor mounting for observing the various testing equipment.

In accordance with the instant invention, the stacks I4 and I6 of the conventional structure are provided with means to absorb the noise created by the motor and propeller to prevent its issuance from the stacks. The means for this purpose comprises a plurality of ribbon walls I8 carried by supporting devices such as I-beams 20, which have their ends supported in opposed walls of the stack. The ribbon walls are each composed of a plurality of sound-absorbing units 22 (see particularly Figs. 2, 3 and 4) superposed one on the other. A number of the units are employed for each of the ribbon walls to extend the ribbon wall from its supporting I-beam 20 to a height which is determined by the noise reduction desired. The ribbon walls, to obtain the most eflicient absorption of sound, are placed as close together as considerations of air flow will permit. For example, they may be spacedV 1 ft. to 2 fton centers.

The units 22 are maintained in their superposed relationship to form a ribbon wall l by any suitable means, such as angle members 50 secured by anchorage bolts or the like 52 to opposed walls of the stacks (see Figs. 4 and 5). Instead of angle members, as shown, the walls may be provided with recesses to receive the edges of the units. In any event, the means suitably presents Aopposed slots or recesses to receive the edges of the units, and in which they may be readily inserted and the units forced downwardly until they contact with the I-beam or a previously placed unit.

The units 22 each comprise a frame including side members Band e'nd members 26, preferably of chann'el shape in cross section with the channels opening inwardly. 'Ihe side and end frame members are secured in assembled relationship in any suitable manner, for example, by welding or bolting at the corners. One or more reinforcing channels 28 preferably connect the side frame members 24 at suitable intervals.

Located within the frame, or, if one or more channels 28 are employed, within each of the frame sections dened by these channels, is a sound-absorbing pad 3l), which in its preferred embodiment comprises two or more layers of a compressible sound-absorbing material, suchas mineral wool felt, hair felt, or the like. In the preferred form, the layers are of unequal thickness and suitably comprise a layer 32 of substantially twice the thickness of the layer 34. Interposed between the layers is a vibratile, air-impervious diaphragm 35 comprising, for example, an asphalt impregnated felt, thin metal sheet, or the like. Perforated facing sheets 36 of a relatively rigid material overle the sound-absorbing pads on both sides thereof and have their edge portions interposed between the side anges 0f the channels and the sound-absorbing pads. Spacing blocks 38 may be located within the frame channels to hold the edges of the facing sheets in engagement with the flanges of the channels. f

The edge of each unit which is to be the lower edge of the unit when the same is assembled in a ribbon wall is provided with suitable 'socket means to engage the upper edge of a unit on which it is superposed. This means (see particularly Fig. 4) comprises lugs 42 secured at suitable intervals by rivets or the like to the channel forming said lower edge. The lugs preferably ilare slightly outwardly to aid in the ready assembly of the units in forming the ribbon walls. In lieu of a plurality of lugs as shown, continuous strips or other types of means for this purpose may be employed. Alternatively, the member 24, to form the lower edge of the unit, may be made somewhat wider than the Vother frame members and have its channel turned downwardly to receive the upper edge of the underlying unit.

'I'he facing sheets each include a multiplicity of closely spaced perforations 4D having a sufficient total area to permit entry of the sound waves into the sound-absorbing material therebehind.

In the assembly of the units to make up the ribbon walls, they are preferably alternately arranged so that with respect to either face of the ribbon wall alternate units expose soundabsorbing felts of greater and lesser thickness, respectively. It has been determined that by this arrangement, a more uniform absorption is obtained throughout the frequency ranges than is the case where the thickness of the absorbing material exposed to the sound is the same throughout the face of the wall.

The facing sheets illustrated in Figs. 2 and 3 comprise corrugated perforated metal or the like. However, as disclosed at 44 in Fig. 6, perforated flat sheets of a rigid material, such as hardened compressed asbestos-cement material. or a Wire mesh screen, as also indicated in Fig. 6 at I46, may be used. Also, expanded metal has been found to be eminently suitable for the facing sheets.

Stacks for a test stand, including the ribbon walls made up of the sound-absorbing units as described above, have been found to be highly effective in reducing the noise issuing from the stacks. The ease with which the ribbon Walls may be built up by merely inserting units in the slots formed by the angle members, or other means, lpermits the ribbon walls to be adjusted to desired heights, as may be required from time to time to secure a predetermined reduction in noise volume upon testing of different types of equipment. Thus, for example, as larger motors or propellers are developed from time to time and tests of the same are required, additional units may be employed to absorb the increased noise, the stacks being extended, if necessary, to accommodate the necessary units. Also, the ribbon walls do not materially impede the air flow through the stacks. To reduce such impedance to a minimum, streamlining members of any suitable type, as indicated at 53 in Fig. l, may be mounted on the I-beams 20. The sound-absorbing units of the type' described are, furthermore, resistant to destructive forces and will not become displaced or damaged by the large quantities of air moving past them at high velocities.

In a modification of the invention disclosed particularly in Fig. 7, units of substantially the channel members as before.

design of that illustrated in Fig. 2 may be employed in lieu of the concrete or masonry outer walls to provide a lightweight, inexpensive, but very substantial construction. Thus, the units 60, forming the outer walls of the stack of Fig. 7, may comprise frame members, which are in all essentials the duplicates of the frame members of Fig. 2 but made of heavier gauge metal if desired. Supported within the frame members is preferably a sound-absorbing pad 30 having its ends extending beneath the flanges of the Also, a sound-pervious facing element of any of the Atypes previously referred to is located to cover the soundabsorbing member on the inner face of the unit. The outer facing member in this instance is made of an imperforate, strong, rigid, weather-resistani; material, suitably a sheet of hardened compressed asbestos-cement material, metal, or the like. The units forming the outer walls are suitably assembled by welding or otherwise joining the contacting faces of adjacent units, as indicated, for example, in Fig. 9. Angle members 62 are secured as by welding to the inner flanges of the frames of units 60, the angle members preferably extending continuously across a plurality of the units 60 to provide channels for the reception of the units making up the ribbon walls similarly as before, and to perform the additional function of reinforcing the outer walls to which they are secured.

A stack constructed according to the above described modification of the invention, in addition to providing a very inexpensive, Weatherresistant, lightweight structure, as previously referred to, increases the sound-absorbing properties of the stack treatment by reason of the fact that the outer walls, as well as the ribbon walls, expose sound-absorbing material `to the sound passing through the stack.

` ribbon walls comprising a plurality of units, eachr The construction disclosed in Fig. 8 is particustraight passages provided by the construction of Fig. 1. In the structure of Fig. 8, the plurality of units making up each of the ribbon walls, the units being of the type previously described, are arranged in zig-zag relationship, the arrangement of the superposed units being such that sound waves cannot pass in a straight, line throughthe stack, but must contact at least a portion of the faces of the units. By this means, adequate absorption is obtained of both the low and high frequency sounds, without, however, providing any substantial impedance to the air passing through the stack.

A further feature of the invention, which may be employed to aid in sound-absorption, particularly absorption of high frequency sounds, and

' which is disclosed in Fig. 8, but which may also be employed in the stack construction of Fig. 1,'

is a baffle or roof member 10 supported in any suitable manner in spaced relationship to the end of the stack, a distance of a foot or more. The baille 'HJ is preferably composed of units of the type previously referred to, including, however, an imperforate outer facing sheet, such as employed in the units 60 forming the outer walls of the construction of Fig. 8. By this construction, not only is a greater absorption efficiency obtained, particularly with respect to high frequency sounds, but also the member 10 serves as a roof or water shed to prevent precipitation from entering the stack.

Having thus described our invention in rather full detail, it will be understood that these details need not be strictly adhered to, but that various changes and modifications will suggest themselves to one skilled in the art, but falling within the scope of the invention as defined by the subjoined claims.

What we claim is:

1. A structure for conducting air having spaced parallel outer walls and a plurality of inner ribbon walls subdividing the space between opposed of said outer walls, said ribbon walls comprising a plurality of removable units, each of said units including a channel frame, a soundabsorbing filling and foraminous facing elements overlying said filling, said filling including layers of compressible, fibrous sound-absorbing material and a vibratile diaphragm interposed therebetween.

2. A substantially vertical stack structure comprising spaced parallel outer walls and a plurality of inner ribbon walls subdividing the space between opposed of said outer walls, each of said including a frame, a sound-absorbing element within said frame and sound-pervious facing elements overlying the face of said sound-absorbing elements, means below said ribbon walls and in alignment therewith for supporting the same, and means carried by said opposed walls for slid- -ablys receiving and supporting the ends of said um 3. A stack structure comprising spaced parallel outer walls and a plurality of inner ribbon walls subdividing the space between opposed of said outer walls, each of said ribbon walls comprising a plurality of removable units, each including a frame, a filling of sound-absorbing material carried by the frame and perforated facing elements comprising corrugated metal sheets overlying said sound-absorbing material, means below said ribbon walls and in alignment therewith for supporting the same, and means carried by said opposed walls for slidably receiving and supporting the ends of said units.

4. A stack structure comprising spaced parallel outer walls and a plurality of inner ribbon walls subdividing the space between opposed of said outer walls, each of said ribbon walls comprising a plurality of removable units, each including a frame, a filling of sound-absorbing material carried by the frame and perforated facing elements comprising a compressed hardened asbestos-cement sheet material overlying said sound-absorbing material, means below said ribbon walls and in alignment therewith for supporting the same, and means carried by said opposed walls for slidably receiving and supporting the ends of said units.

5. A stack structure comprising spaced parallel outer walls and a plurality of inner ribbon walls subdividing the space between opposed of said outer walls, said ribbon walls comprising a plurality of removable units, each of said units including a frame, a sound-absorbing element within said frame, and perforated facing eleinterposed therebetween, said plurality of units in each of said walls being so arranged that at a face of the wall alternate units expose a thicker layer and intermediate units a thinner layer of the sound-absorbing material to the sound to be absorbed.

6. A substantially vertical stack structure comprising spaced parallel outer walls and a plurality of inner-ribbon walls subdividing the space between opposed'of said outer walls, said ribbon walls comprising a plurality of readily removable units, each of said units including a frame, a filling of sound-absorbing material carried by the frame, and a porous facing element overlying said sound-absorbing material, guide means for slidably receiving the ends of the units comprising a ribbon wall, means below the ribbon walls and in alignment therewith for supporting the same, and means on each of said units for maintaining the unit in aligned relationship with respect to a vertically adjacent unit.

7. A sound-absorbing unit comprising a frame, a plurality of layers of readily compressible, fibrous sound-absorbing material supported within said frame and a flexible, vibratile, substantially air-impervious diaphragm interposed between said layers.

8. A sound-absorbing unit comprising a closed frame, a plurality of layers of readily compressible, fibrous sound-absorbing material of different thicknesses within said frame and a vibratile, flexible, substantially air-impervious diphragm interposed between said layers.

9. A stack for a test stand comprising perma nent outer Walls including opposed walls in parallel relationship, means carried by said opposed walls for supporting a plurality of spaced parallel ribbon walls thereon, means carried by said opposed walls in alignment with said supporting means for slidably receiving a plurality of units to constitute each of said ribbon walls, said units comprising a frame, a sound-absorbing filling and perforated facing sheets overlying said filll0. A stack structure comprising spaced para1- lel outer walls and a plurality of inner ribbon walls subdividing the space between opposed ol' said outer walls, said ribbon walls comprising a plurality of sound-absorbing units with the units of adjacent walls lying in substantially parallel relationship and at angles to the units thereabove and therebelow.

11. A stack for a test stand comprising outer walls including opposed walls in parallel relationship, means carried by said opposed walls for supporting a plurality of spaced ribbon walls, said ribbon walls each comprising a plurality of units consisting of a frame, a sound-absorbing filling and perforated facing sheets overlying the filling, said units in each wall lying in substantially parallel relationship to the units of adjacent walls and at angles to the units thereabove and therebelow.

JOHN S. PARKINSON. WILLIAM I. LUCIUS. 

